TIME -- The human papillomavirus (HPV) vaccine Cervarix, produced by GlaxoSmithKline, offers protection against the two major cancer-causing strains of HPV, (HPV-16 and HPV-18) for more than 6 years, according to research published online today in the British medical journal the Lancet. The analysis, led by Dr. Cosette Wheeler from the University of New Mexico, included more than 1,000 women between the ages of 15 and 25, who had normal cervical cells and no evidence of HPV infection at the study's onset. Roughly half of the women were given the Cervarix vaccine, and half given a placebo. Ultimately 700 women across three nations completed the study, which included HPV screenings every six months for up to 6.4 years. At the end of the study period the researchers found that, not only did the vaccine protect against HPV-16 and HPV-18 for the full duration of the follow-up, but it also protected against HPV-31 and HPV-45, two additional strains of the virus that are responsible for 10% of cervical cancer cases.